Phased-array antenna systems are used in a variety of communication applications. A phased-array antenna system generally includes an array of antenna feed elements that emits and/or receives radio frequency signals by forming a beam that can be steered through different angles. Through controlling the manner in which the signals are emitted or received, the direction may be changed. The changing of the direction is also referred to as steering.
One example of a typical application of phased-array antenna systems is on communication satellites. These communication satellites are often used on wireless communication platforms for remote, hard to access, or mobile user terminals, e.g., mobile platforms, to provide service coverage over large geographic footprints, often including remote land-based or water-based regions. Generally, base stations (e.g., ground base stations) send information (e.g., data) to the user terminals through a bent pipe system using one or more satellites. More specifically, the base stations send information on a forward link to the satellite that receives, amplifies and re-transmits the information to an antenna of one or more fixed or mobile user terminals. The user terminals, in turn, can send data back to the base stations via the satellite. The base stations can provide the user terminals with links to the Internet, public switched telephone networks, and/or other public or private networks, servers and services.
Modern satellites and other cellular communication systems often employ a number of spot beams providing a beam laydown that forms coverage over a geographic region that may be divided into a plurality of cells. In a communication system using spot beams, the same frequency may be used at the same time in two or more cells. These beams may be configured to maintain a predetermined co-polar isolation (e.g., carrier-to-interference ratio) value in order to minimize the interference among beams. This is called spatial isolation and spatial reuse. In one typical parlance, each spot beam may be assigned a color to create a color pattern that matches a frequency reuse pattern. Identical frequencies, then, may be reused by different beams with the same color.
The phased-array antenna systems of satellite and other communication systems often suppress interference by employing adaptive beamforming techniques. Traditionally, these adaptive phased-array antenna systems utilize a receiver in each of its antenna feed elements, signal correlators, and a central processor to dynamically mitigate interference. Fully-adaptive algorithms employed in these systems, such as the Howells-Applebaum algorithm, typically maximize signal-to-noise ratio (SNR) or minimize received antenna power to achieve performance gains. In many adaptive phased-array antenna systems, the signals at each antenna feed element must be determined accurately to effectively place nulls at sources of interference (sometimes referred to as interference sources, interferers or the like). This drives a requirement for one receiver per antenna feed element and an extensive calibration system, which dramatically impact cost and feasibility for most applications requiring large phased arrays.
An alternative to the aforementioned fully-adaptive arrays utilizes an iterative process that relies on using a constellation pattern of only a subset of the antenna feed elements with imposed weight constraints. These weight-constrained iterative algorithms eliminate the need for element receivers as in fully-adaptive algorithms. But performance of these systems is limited by the low quantity of antenna feed elements that form the cancellation pattern, especially in scenarios where interferers are situated in close proximity to desired signals.